The dates for the Tunney’s Pasture hazardous waste depots are now known, Sunday, May 6 2018 and Sunday, September 16 2018. See the city web site https://ottawa.ca/en/residents/garbage-and-recycling/hazardous-waste-and-special-items for a list of the items that are considered too hazardous for regular garbage (things like mercury filled fluorescent light bulbs).
If you have electronic waste (old computers, TVs and other equipment) or fabrics you want to get rid of, Connaught Public School (Rosemount and Gladstone) http://connaughtschoolyardrenewal.ca/ (oddly not listing their own event for this year, though it is listed in http://www.recycleyourelectronics.ca/) is taking them to help raise funds for school yard improvements. Electronics and textile recycling on Friday April 20 from 7:45 to 8:30 am and Saturday, April 21 from 8 am to 1 pm.
The city also has a list of other e-waste events. I see there is one nearby at Dovercourt on Saturday, April 14 2018, 10 a.m. to 4 p.m.